The SIR provided I -Te-Met; . 1 OOg This project is using X-ray crystallography to determine the structure of proteins from the hypothermophile Pyrobaculum aerophilum for which the complete DNA sequence has been deten-nined. Te-methionine is being used new rational approach to phasing crystallographic data. Te-methionine specifically replaces the naturally occurring amino acid methionine Tellurium (Te) is a heavy atom with a strong anomalous signal that is useful for phasing crystallographic data. The first protein we are applying the Te-methionine is a histone-like protein that binds to the DNA.This protein stabilizes the DNA double helix at the high growth temperature of this hyper thermophile.